More than just a refuge for insomniacs, late night telly has helped hatch a movie idea or two in its time. The latest to tiptoe out of the wee smalls and onto the big screen came when George Clooney stumbled upon an obscure Dutch film about Hitler's systematic pillaging of Europe's fine art to decorate his own personal Reichmuseum. "I'd seen The Train [and] had caught, late one night, The Rape Of Europa, so I knew something about Hitler ripping off all the art," he told Empire. "Which was one of the reasons he didn't bomb the hell out of Paris." The writer-director-star talked about how the film came about, its inspirations and his strategy for snaring the elusive Bill Murray.

Why make The Monuments Men? What piqued your interest?Grant (Heslov) and I were sitting around, it was after we had done Ides Of March, and were working on Argo, and I was thinking, "Well, what am I going to do next - what are we going to do as our next project? And he said, 'Well, I read The Monuments Men, and it's a really interesting book.'" So I read it, and we started talking - this was actually one of those old-fashioned Hollywood movies, in a real sense of the word. You know: a true story in which a bunch of misfits, all non-soldiers, get together and have to go into the middle of a war zone. There they try to tell their own men not to blow things up, and find out the extent of Hitler's greed. It is extraordinary: he was going to steal everything. The fact that it was extensive as it was made it that much more interesting.

Robert Edsel's book is a very disparate story, spread over a large field. How did you find the story?That is the job of adapting something. If you'd seen (Beau Willimon play) Farragut North, it doesn't really read as a movie. You have to create things to make it cinematic. Obviously, the first thing we had to do was fictionalise some of the characters and to give them flaws, because we didn't want to give flaws to real people. That is not particularly the kindest thing to do. And you want to keep as much of the truth as you can, but you also want to make it a movie - art is not something that is necessarily sexy. So we had to tie pieces of art to the characters, and you have to care about the characters; if you care about the characters, then you care about the art as well. That's moviemaking.

Tell us about the tone of the film.There are certainly fun elements in it, there have to be otherwise it doesn't work as a movie, but those old WW2 guys had a very different kind of humour. Six of my uncles were in the war. There is a sort of a dry humour to some of the stuff that goes on, but people get killed and there's a real drama to it, once you place a time clock on it. It's not Ocean's Eleven. I'm not saying that as an insult to Ocean's Eleven, you just have to understand the tone of it.

You mentioned The Train. Were there other movie touchstones you went to for inspiration?Yeah, I looked at '60s and '70s World War II films: The Great Escape, The Guns Of Navarone. A lot of films you remember as being really fantastic are dated. Films from the other side of the hemisphere, like Bridge Over The River Kwai, play pretty well, and there are really wonderful moments in a lot of those films. But what you are really looking for is a straighter version of the war, because some of those films could be goofy funny. We wanted to have some fun with it, but we looked at a lot of movies like a Bridge Too Far, because those are the movies I grew up loving...

How easy is it to maintain a big cast, in the sense of creating throughlines and balancing things?Well, you do a lot of that work in the screenplay before you get there. You have to be very specific, having a lot of well-known actors who are only going to do these parts if they think their characters are well served. They don't want to be the guy standing in the background, they want very specific storylines. We worked for a long time with most of these actors in mind and dealt with it during the screenwriting process. But getting out on location, and also directing myself, you do reach a stage where you wish you weren't acting. It isn't so easy to be doing a scene and then finish, say "cut!", run off to the monitor, watch the scene quickly and then come running back to the scene, thinking you could do better in it. It's a lot of dancing around, which gets to be, I imagine, comical for other people to watch.

Were you going to be in it front the start or was there a point where you decided to take the part?Well, look, it's about these men who are past their prime doing things that seemed sort of perfect for me actually. I always thought I was going to play what in the book is the (real-life art conservationist) George Stout role, although we changed the character's names obviously. I always felt that I was going to play the guy who rounded them all up in the beginning, because it felt like something I could do. And it seemed , quite honestly, if I was casting as a director I would offer it to myself. I wrote Good Night, And Good Luck with the interest of playing [Edward] Murrow, but then we read and I realised I was the wrong actor to play that part. There is a hardness to Murrow that isn't naturally given to me in general, and I didn't think I could act my way out of it, so we went looking for people and luckily got David Strathairn. If I was casting this, just as a director, I'm probably one of the right people for the part.

And you snared the elusive Bill Murray. How did you manage that?Well, Bill and I have been really good friends for a while now. He comes to my house in Como in the summer for a couple of weeks and we play basketball. We really enjoy each other's company. In the summer of 2012 Grant (Heslov) and I were in the middle of writing the screenplay and we hadn't told him we wanted him to play a part yet. So I called him, last October or something, and said, "Well, we've finished the screenplay and want to send it to you." And he called me and said, "When you guys were talking about this, I wanted to say, 'Hey, can I play a part in it?' So I'm really happy." I wish you could have seen what it was like with him and John Goodman on set. We had absolutely the worst weather you have ever seen - it was snowing in May - and Bill and John would be sitting on set, even when they weren't in the scene, and they'd be picking up camera boxes and helping the crew move stuff. It felt like those old Andy Hardy "let's put on a show" things.

It sounds as if you have really enjoyed this one? We had a great time because it really was a lot of work to do what was required for this. I had a big part in the movie, and with the weather preventing us from shooting outside, we were rewriting every night to move locations - it definitely wasn't snowing in May 1945. So it was really helpful to have a lot of this cast, where every single member wanted to help and there was a camaraderie. It happens when you work with really good people.

If you could show your film to the original Monuments Men, what would you hope they'd say?Well, I think what they would love about it is that we captured the spirit of exactly what they are trying to do. That was the most important part, to save this culture. We captured their qualities of these men who had a different language from a different time: you didn't talk so much about your feelings. A lot of people were dying, a lot of bad things were going on but you just kept going. They'd also be pleased that about 70 per cent of the story is completely factual. It doesn't often happen in films like this, because you end up throwing out facts in exchange for story points. More than anything, though, they'd be happy that we are bringing attention to the thing that mattered most - not just the art, because art seems like a civics lesson, but actually who they are, and what they were made of, and what they were willing to die, and did die, for. I hope they would enjoy that we appreciated that.

One of the interesting themes is this idea of 'Nazi logic'. They hungered after the beauty of art yet still killed millions.Well, it's amazing when you see how careful they were - for instance, in hiding art in salt mines a mile down. They took greater care in preserving art they had stolen, art created by their perceived enemies, than their own citizens by the end. It is an amazing contradiction, of course. Hitler had a giant model of the Fuhrer museum he was going to build which he'd constantly visit, even in the bunker at the end. He wrote about it in his last broadcast: "Even though I die, the Fuhrer chamber should go on." He wanted it all to belong to him, just as Napoleon did. It's just amazing what he believed he was going to get away with.

Has the experience made you appreciate art more?I wasn't a great connoisseur of art, as you can imagine, and it was quite a learning process. But saying that, it absolutely made me appreciate art and architecture. But the main thing was that it made you understand that what these pieces of art are, their connection to our history. That is the thing that gets lost sometimes when you talk about art, you forget that these were moments in time that point out mans' greatest achievements - and you have to have that record somewhere, that can be in monuments, it can be in sculptures, it can be in paintings, it can be in writing, it can be in any of these pieces.